The resonator fiber optic gyroscope (RFOG) has potential fulfilling needs across many gyro and inertial navigation markets because of its high performance in a small size and at low cost. FIG. 1 illustrates a conventional RFOG 10 consisting of a clockwise (CW) laser 12, a counter-clockwise (CCW) laser 14, a fiber optic resonator 16 and electronic circuits (“electronics”) providing at least resonator-coupling and resonance-tracking (or resonance-detection) functionality. The CW laser 12 inputs light into the resonator 16 and a CW photodetector 18 detects the CW output of the resonator.
The electronics downstream of the CW photodetector 18, which include a CW modulation generator 20, a CW demodulator 22, a CW integrator 24, and a summing element 26, control the CW laser frequency to a resonance frequency of the resonator 16. The resonance frequency is detected by modulating the laser frequency at f1 using the CW modulation generator 20 and then demodulating the output of the CW photodetector 18 at f1 using the CW demodulator 22. At the resonance frequency, the CW photodetector 18 signal at f1 passes through zero amplitude. The CW integrator 24 controls the laser frequency via the CW laser driver 38 to the resonance frequency by adjusting the laser frequency until the output of the CW demodulator 22 is zero. The modulation at f1 is electronically summed with the CW integrator 24 output by the summing element 26. The CCW laser 14 is controlled to the CCW resonance frequency in a similar manner, except it is common that the modulation frequency f2 is different than f1 to eliminate errors that arise when light from one direction of propagation in the resonator 16 inadvertently couples into the other direction.
One major limitation of RFOG performance comes from distortion of a modulation required for rotation sensing. The IFOG has a unique property called the eigenfrequency, at which rotation sensor errors due to modulation distortion diminish to zero. The RFOG does not have an equivalent eigenfrequency. Ultra low distortion electronics help, but are typically not good enough to meet distortion-limiting requirements.